Horn problems

my horn doesn't work. The old one had two terminals and according to the circuit diagram takes power from the fuse box, direct to T1 and then back from T2 to the horn button which makes a contact to earth. The body of the horn is also grounded. But, if I connect my new, aftermarket, non Haf horn, it doesn't work. If I connect the new horn to a battery and apply power to T1 and earth to T2 it blasts out. If I apply power to T1 and earth the body nothing happens. I used a meter to try and measure the volts in the two red wires that feed the horn. Neither gives more than .5 of a volt, and neither seems more 'connected' than the other. What am I not understanding about this. The circuit seems quite clear and I would have expected at least one of the two feed wires to have a good, if not 12, volt indicated. Any suggestions please?

Nigel

Comments

I don't have my wiring diagram to hand, but going from memory and the fact the wiring is relatively simple, I would make the following suggestions.

The power for the horn needs to go via the horn button in the steering wheel. The has a red wire running up the middle. The ring in the middle of the button, when pressed makes an earth connection to the outside ring which is the metal tube of the steering column. So the wire up the centre gets twisted every time you turn the steering wheel - possibly it has a break / bad connections.

The red wire, I think, goes direct to one of the terminals on the horn. The other goes up to the fuse box and finds a fuse. Other side of the fuse should be a live 12 volt supply.

The fuse box connections could be dirty / loose which would give you poor voltage when you measure between them and earth.

Clean the connections on the fuse box, check the cable going up the centre of the steering column for continuity. Check the horn button for corrosion under the horn ring.

Just remember the horn body is isolated so only connections are the two terminals T1 and T 2. It does not matter which one is connected to earth or to power. Also the switch (horn button) can be on either side of the circuit - i.e. it can earth the horn or it can supply power to the the horn.

I'll dig out my wiring diagram this evening and have a look to see which side it thinks it is fitted.

Failing all of this, we can sort it out at Eastwell Park this weekend.

Maybe there is a short in the red wire that comes up the steering wheel shaft, causing insufficient volts to go through the horn button. I'm not sufficiently electro-boffery to know how to work out whether there is a short, but maybe feed in a new good wire down the shaft if you can?

Thanks both. I have a spare,ish day tomorrow as apart from the horn and collecting my seat squabs I am ready for the Treffen so I will have another look. I did measure the red wires at the horn with the (new) button pressed and got b' all so I will have a look at the column wire and the due box and see if I can find it. The joys of owning an old car. I used to have a 1971 lotus 7 and I swore after I sold it I would never get another old car again. Mmmmmmm.

If you are going to replace the wire running down the steering column, I would use some thing called "ExtraFlex" wire - same sort of wire as used for multimeter probe cables. It does not work harden like ordinary copper wire so will survive much longer being turned round and round in the steering column. Can be bought from somewhere like Maplin's or online.

If you are re-wiring, decide if you want the horn to be live when the ignition is off or only when the ignition is on ( I would go for always live myself).

Run a wire from the fuse bow to one of the terminals on the horn. Run a wire from the other terminal on the horn up the centre of the steering column to the horn button.

Make sure the outer ring of the horn button has a nice clean connection the metal of the steering column,

Horn should now work.

If it does not, try taking a piece of wire and connecting the metal of the steering column to the platform body - obviously bright metal to get a good electrical connection.

Sometimes things are much simpler than you might think. In the end the old horn was kn.......red and was blowing the fuse. Aha you might say, why didn't I check the fuses first. Which of course I had done. But I only checked the fuse panel on the dash. On a Polycab there is a secondary, two fuse unit under the dash that I always thought was just for the ignition as it has a 25 amp fuse in it. Wrong. The second fuse, 8 amp, is for the horn. Replaced and bingo, now have power to the new horn. But then it got a bit more entertaining. Every time I turned the steering wheel the horn sounded. Mk1 fix, disconnect the horn. Subsequently found that the new horn button has a lug on the side that is meant to slot into a groove in the boss that I don't have on mine. So all it needs is the lug removing and the horn will sit flat in the boss and not make to earth when I turn the wheel anymore. Aren't Haflingers such fun.